The objectives of the proposed research are to delineate the characteristics of several homeostatic transport systems (Na, K, Cl, HCO3/H) in the choroid plexus of the rat at various stages of development. Information concerning the development of these systems will be obtained by analyzing the effects on ionic transport of alteration in the activity of two transport enzymes in the choroid plexus: Na-K-ATPase and carbonic anhydrase by inhibitors such as ouabain, acetazolamide and amino-reactive agents. On the basis that a substantial change in ionic transport across a cell membrane is reflected as a change in cellular concentration of the ion, the general approach will be to ascertain the nature of drug-induced changes in the concentrations of ions in the epithelium of the plexus. Cellular concentrations will be calculated from compartmentation data. Data for choroid plexus will be correlated with corresponding data for cerebrospinal fluid for the purpose of constructing models for the transport of ions across the blood-cerebrospinal fluid barrier. The data obtained should enhance our understanding of the role of epithelial cell transport in the central nervous system in producing a stable micro-environment for the neural cells in both immature and mature mammals.